So-called gas spring assemblies have numerous applications in the tooling industry, and are typically integrated into various types of specialty tooling, dies and molds. For example die springs may be used in stripping operations, to even out pressures on stripper plates; in progressive dies used for drawing operations; for forming in two directions; for cam returns, in inverted drawing operations; and, in floating punch operations. These gas spring assemblies typically comprise an outer tube or cylinder within which there is slidable a piston or rod defining a gas pressure chamber which is normally filled with a fixed volume of a suitable gas, such as nitrogen. The fixed quantity of gas within the pressure chamber normally biases the piston/rod outwardly, but of course is yieldable to allow retraction of the spring/rod in a spring-like manner. The outer end of the rod bears upon various tooling, dies, or molds as discussed above. In many applications, it is important that the extended length of the rod relative to the cylinder remain constant since other dimensions of the tooling, die, molds or the equipment upon which they are mounted, are dependent upon the extended length of the spring assembly.
Prior spring assemblies of the type discussed above often employ a special type of seal to prevent escape of the pressurized gas along the outer walls of the rod or cylinder. These seals typically comprise a relatively soft, flowable seal packing surrounding the piston/rod, composed of PTFE and silicone lubricant, captured between a pair of opposing seal caps. The soft seal packing material is biased into sealing engagement with the piston/rod when an axial force is applied to the seal which results in axial compression of the seal caps. Repeated operation of the gas spring assembly over time results in axial compression and eventual consumption of the seal because of the consumable nature of the soft sealing material. Consequently, in the past, seals of the type described above have been mounted in a seal housing surrounding the piston/rod which is arranged such that it shifts axially to compensate for axial compression of the soft seal packing material. However, because it is necessary to expose one end of the seal housing to gas pressure, this end of the seal housing is also exposed to the piston (or a shoulder of the piston) which actually engages the seal housing when the piston/rod is fully extended. Because the end of the seal housing acts as an outer stop to limit the maximum outward extension of the rod, the extension length of the rod eventually increases as the seal housing axially shifts over time as the seal packing material is consumed, thus diminishing the operational accuracy of the gas spring assembly.
Prior gas spring assemblies also possess a number of other shortcomings which are subject to improvement, including the need for improving manufacturing assembly of the gas spring, the ability to quickly disassemble the gas spring for maintenance and the need to provide a means for adjusting initial axial loading of the seal.
The present invention is directed toward providing solutions to each of the deficiencies mentioned above.
It is therefore a primary object of the present invention to provide a gas spring assembly of the general type described above which is not subject to degradation of accuracy due to alterations in the maximum extended length of the spring rod.
Another object of the invention is to provide a gas spring assembly as mentioned above which substantially reduces the need for maintenance and/or facilitates maintenance of the gas spring assembly due to wear.
A further object of the invention is to provide a gas spring assembly as mentioned above which is easy to assemble and disassemble.
A still further object of the present invention is to provide a gas spring assembly of the type using a consumable, compressible seal in which the cylinder/rod is precluded from axially bearing on either the soft seal or the seal housing containing the seal.